PHP5中虚函数的实现方法分享_php教程-查字典教程网
PHP5中虚函数的实现方法分享
PHP5中虚函数的实现方法分享
发布时间:2016-12-29 来源:查字典编辑
摘要:请看下面的代码:复制代码代码如下:该例中,A::y()调用了A::x(),而B::x()覆盖了A::x(),那么当调用B::y()时,B::...

请看下面的代码:

复制代码 代码如下:

<?php

class A {

public function x() {

echo "A::x() was called.n";

}

public function y() {

self::x();

echo "A::y() was called.n";

}

public function z() {

$this->x();

echo "A::z() was called.n";

}

}

class B extends A {

public function x() {

echo "B::x() was called.n";

}

}

$b = new B();

$b->y();

echo "--n";

$b->z();

?>

该例中,A::y()调用了A::x(),而B::x()覆盖了A::x(),那么当调用B::y()时,B::y()应该调用A::x()还是 B::x()呢?在C++中,如果A::x()未被定义为虚函数,那么B::y()(也就是A::y())将调用A::x(),而如果A::x()使用 virtual关键字定义成虚函数,那么B::y()将调用B::x()。然而,在PHP5中,虚函数的功能是由 self 和 $this 关键字实现的。如果父类中A::y()中使用 self::x() 的方式调用了 A::x(),那么在子类中不论A::x()是否被覆盖,A::y()调用的都是A::x();而如果父类中A::y()使用 $this->x() 的方式调用了 A::x(),那么如果在子类中A::x()被B::x()覆盖,A::y()将会调用B::x()。

上例的运行结果如下:

A::x() was called. A::y() was called. --

B::x() was called. A::z() was called.

virtual-function.php

复制代码 代码如下:

<?php

class ParentClass {

static public function say( $str ) {

static::do_print( $str );

}

static public function do_print( $str ) {

echo "<p>Parent says $str</p>";

}

}

class ChildClass extends ParentClass {

static public function do_print( $str ) {

echo "<p>Child says $str</p>";

}

}

class AnotherChildClass extends ParentClass {

static public function do_print( $str ) {

echo "<p>AnotherChild says $str</p>";

}

}

echo phpversion();

$a=new ChildClass();

$a->say( 'Hello' );

$b=new AnotherChildClass();

$b->say( 'Hello' );

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